The present invention relates to a sorbent cartridge especially useful for solid phase extraction but having applicability in other areas. Solid Phase Extraction (SPE) is a widely used sample preparation/purification technique applied for complex samples such as natural product extracts and body fluids. This technique uses small separation columns (cartridges) which contain a layer of sorbent material. The components of a sample passed through this layer of sorbent material are either retained on the surface of the sorbent material or pass through the sorbent material unretained. The nature of the sorbent material is usually chosen such that the components of interest are retained in the sorbent cartridge and those that pass through are either not of interest, or the failure to be absorbed indicates the absence of a particular component. The absorbed component is released during a later processing step for subsequent processing and/or analysis.
Commercially available SPE cartridges are available in various sizes, usually with an internal diameter of 5 mm and up, an internal volume of minimum 1 ml and contain 100-200 mg of sorbent material. In exceptional cases such cartridges can hold 25-50 mg of sorbent. Recently released SPE equipment operates plastic plates with 96 wells, each well containing 10-15 mg of sorbent material.
SPE cartridges are made by placing a first porous disk or glass or silicone wool at the bottom of the cartridge and then filling the sorbent material from top of the cartridge. The layer of sorbent material is kept in place with a second porous disk placed on top of the sorbent material. During use, the fluid sample, the wash and the extraction fluids are passed through the SPE cartridge from top to bottom, i.e. in the direction of gravitational forces. The fluid sample penetrates through the layer of sorbent material due to gravitation or centrifugation, or because of pressure or vacuum applied to the cartridge with various accessories, but the direction of flow is along the direction of gravity from the top to the bottom and then out an opening in the bottom.
An improved sorbent cartridge for use in preparing fluid samples for chemical analysis is provided by placing sorbent into a pipette tip at its distal end and sucking fluid to be analyzed into the sorbent with a setter. This mode of use reverses the fluid flow of a normal sorbent cartridge. The sorbent cartridge is formed from a pipette tip having a longitudinal axis and a tip with tapered interior having walls defining a cavity extending along the axis and opening at a distal end of the tip. A porous barrier is placed in the tapered cavity at a predetermined location in the tip to define a sorbent volume between the barrier, the cavity walls and the opening at the distal end of the tip. The barrier allows processing fluids to pass through the barrier. A sorbent material is placed in the sorbent volume. The sorbent material is preferably selected for use in chemical analysis and the barrier being selected to prevent passage of the sorbent material. This construction is adapted for use by applying a reduced pressure to draw or suck the fluid to be analyzed against the direction of gravity, through the tip of the pipette, through the sorbent and then through the barrier filter. This cartridge is especially suitable for preparing samples for chromatographic analysis, but has broader applicability.
Variations to this basic sorbent cartridge can be made. These variations include the addition of means for exerting suction on the pipette to draw processing fluids through the opening in the tip, through the sorbent material and through the filter. A manually operated syringe structure or a pipette can achieve this. The syringe preferably comprises a setter in fluid communication with a second opening opposite the opening in the distal end. The setter is configured to mate with the second opening to place a first cavity in the setter in fluid communication with the filter. A plunger is slidably received in a second cavity in the setter and placed in fluid communication with the first cavity. The plunger and first cavity are sized relative to each other so as to create a suction sufficient to draw fluid from the opening in the tip into the cavity in the setter when the plunger slides in the second cavity.
Preferably, the size of the opening in the tip is from about 2 to about 10 times the size of the material used in the sorbent material. Further, the sorbent material is placed in the cartridge by drawing a mixture of a solvent and the sorbent material through the opening in the distal end of the tip, with the solvent passing through the filter to leave the sorbent in the sorbent volume. The sorbent material itself preferably has a coating of a solvent that is sticky enough to cause sorbent material to stick together and resist passage out of the opening in the tip. The solvent is preferably one of glycol or ethylene glycol, which do not adversely affect most analytical methods.
Advantageously, the sorbent volume comprises a tapered volume tapered toward the distal opening, and the porous barrier comprises a frusto-conical filter of similar shape, aligned to fit into and wedge into the tapered volume.
Another aspect of this invention comprises an apparatus for analysis of fluid samples, preferably for use in chromatography. The apparatus comprises a hollow tip having an opening in a distal end and means in the tip for retaining a porous barrier at a predetermined location to define a sorbent volume between the barrier and the opening in the hollow tip. A sorbent material is retained in the sorbent volume by the porous barrier, with the barrier allowing passage of fluids but not the sorbent material, during use of the apparatus. Suction means are placed in fluid communication with the hollow tip to suck fluid through the opening in the distal end and through the sorbent material and porous barrier.
The invention further comprises a method of forming a sorbent cartridge. A porous barrier is placed at a predetermined location in a hollow tip of a pipette to define a sorbent volume between the barrier and opening in a distal end of the tip. A slurry of sorbent and a fluid is sucked or drawn into the sorbent volume through the opening in the distal end of the tip until the volume is filled with sorbent. The solvent is further sucked through the barrier while the barrier prevents passage of the sorbent. The solvent is selected so that it does not degrade later use of the sorbent for chemical analysis. This method advantageously allows the fast formation of a sorbent cartridge with a high accuracy of the sorbent volume.
This basic method is further varied by sucking a washing fluid through the opening, sorbent and barrier to remove undesired materials from the sorbent. Additionally, at least one cap can be placed on the tip to help prevent degrading the performance of the sorbent. The method further comprises the step of placing a syringe suction device in fluid communication with the tip to exert a reduced pressure that draws fluids through the opening, sorbent and barrier and into the syringe. Alternatively, the method can comprise the step of placing a syringe device in fluid communication with the tip to exert a positive pressure that forces fluids through the barrier, sorbent and opening. As with the apparatus, the method preferably leaves a coating on the sorbent that causes the sorbent material to stick to each other and resist falling out of the opening. That coating is achieved by using a solvent selected from the group comprising glycol and ethylene glycol.
There is also provided an improved method of forming and using the sorbent cartridge for chemical analysis. This method allows easy formation followed by immediate use, which has advantages in some applications. This method comprises the steps of placing a porous barrier at a predetermined location in a hollow tip of a pipette to define a sorbent volume between the barrier and opening in a distal end of the tip and sucking a slurry of sorbent into the sorbent volume through the opening in the distal end of the tip until the volume is filled with sorbent and sucking the solvent through the barrier while the barrier prevents passage of the sorbent. The solvent is selected so that it does not degrade later use of the sorbent for chemical or chromatographic analysis. A fluid sample to be analyzed is then sucked through the opening and into the sorbent to interact with the sorbent. Most of the fluid sample is withdrawn through the barrier except for the components retained on the sorbent. Advantageously, the sample components retained on the sorbent can be extracted from the sorbent by passing another fluid thorough the sorbent, by collecting this fluid in the setter and by transferring it into a removable container for further analysis or processing. Alternatively, by applying a positive pressure through the barrier into the sorbent the sorbent can be expelled out the opening for further analysis or processing of the sorbent after it has interacted with the fluid sample. In this case the directing of fluid flow is in the direction of gravitational forces.
The above methods and apparatus provide many advantages. One advantage of this invention is to provide a sorbent cartridge, which is made of commercially available pipette tips, or a similar conical body holding a small volume of sorbent material in the tip.
Another advantage of this invention is to provide a cartridge used for SPE filled with a sorbent underneath a porous layer that keeps the sorbent material in place during the filling of the tip and after the tip has been filled.
Another advantage of this invention is to provide a cartridge, which may release the sorbent into a vial or reaction vessel for further sample preparation and/or analysis.
Another advantage of this invention is to provide a sorbent cartridge, which may be made by an automated sample preparation instrument right before use in the shortest time.
Another advantage of this invention is to provide a sorbent cartridge, which allows for small sample volumes to be prepared for analysis by requiring small amounts of reagents and by reducing sample dilution to minimum.